The fabrication of semiconductor devices on substrates typically requires the deposition of multiple metal, dielectric and semiconductor film layers on the surface of the substrate. The film layers are typically deposited onto the substrate in vacuum chambers. Certain processing operations require that the deposition of multiple film layers or the etching of a previously deposited film layer. During these processing steps, it is necessary to properly align and secure the substrate in the processing chamber in which the desired deposition or etch process is performed.
Typically, the substrate is supported in the chamber on a support member, commonly referred to as a pedestal. The substrate is placed on, and secured to the upper surface of the pedestal prior to the deposition or etch process. In one process, metal may be deposited onto the back side of the substrate following processing of the front side of the substrate. During this type of processing operation, the substrate is supported on rest buttons which extend from the upper surface of the support member to reduce the surface area contact between the substrate and the support member. The rest buttons are sized and positioned to locate the substrate at a desired location in the chamber. To ensure proper processing of the substrate, the substrate must be properly aligned relative to the support member and a generally planar surface must be presented for the receipt of the deposition layer. The position of the support member in the chamber is selected to provide a desired spacing and relative geometry between the generally planar surface of the substrate and portions of the process chamber. In a sputter deposition process, for example, the position and alignment of the substrate is selected to present a planar surface of the substrate co-planar to the planar target surface, and at a distance from the target which is selected to provide uniform thickness deposition on the substrate.
Substrates onto which film layers are deposited may be extremely thin. Thin substrates tend to warp or take on a "potato chip" profile. When the substrate warps, it no longer presents a generally planar surface to receive deposition material. The warped surface of the substrate results in a non-co-planar relationship between the substrate and the target, and variable spacing therebetween. Consequently, in applications where substrates have become bowed, the substrates must be flatted before they are exposed to the deposition environment. Otherwise, non-uniform thickness deposition of the film layer may result.
In order to hold the substrate in a fixed position and to flatten warped substrates, a clamp ring is used to clamp the substrate (wafer) to the pedestal. Care must be taken in securing the substrate so that the substrates not damaged by the clamp ring. Clamp rings must be positioned both laterally and vertically relative to the substrate to ensure that the substrates are not damaged under the weight of the clamp ring or by contact between a misaligned substrate and a clamp ring as the substrate contacts the clamp ring. Typically, clamp rings also function to assist in aligning the wafer on the support member. To achieve such alignment, the clamp ring is provided with wing members that extend downwardly and outwardly from the clamp ring in order to funnel the substrate into alignment with the clamp ring and the pedestal. Consequently, vertical and lateral forces are applied to the substrate as the wing member achieves lateral alignment and the clamping portion simultaneously achieves vertical alignment of the substrate, clamp ring and pedestal as the clamp ring settles onto the pedestal.
In processing systems such as CVD, PVD, and etch processes, clamp rings also provide shielding to prevent airborne materials from depositing on the interior surfaces of the chamber. Shield arrangements have been devised to restrict the processing environment to a region adjacent to the surface of the substrate. A typical shield system includes a fixed wall portion which extends between the outer chamber cover at a position within the chamber where the pedestal is positioned during a processing period. The fixed wall portion extends around the circumference of the pedestal when the pedestal is positioned for processing, and thus blocks access of the processing environment to the walls and interior components with the chamber.
Several designs of clamp rings have been devised in the past to suit the needs of processing operations and geometries of specific processing chambers. Clamp rings may be either continuous rings which engage the entire peripheral top surface of a wafer, or intermittent finger-like pads which peripherally engage portions of the top surface of the wafer and urge it against the underlying pedestal.
The application of clamping pressure by surfaces of the clamp that engages the periphery of the wafer can result in several processing problems that affect the quality of the processed wafer. For example, moving contact between the clamp ring and the outer edge of the wafer during the clamping process sometimes results in small pieces of the wafer being broken off which are then carried onto the surface of the wafer during processing of either that, or subsequent wafers. Such particles act as contaminants on the wafer surface, which become buried in the wafer during subsequently deposition processes. Such defects can result in streamlines, crazing, metal photo-defocusing during subsequently processing and metal line ridging, all of which reduce yield and through put of the processing operation.
Similar defects can result from imperfections in the pad surfaces on the clamp ring that engage the outer peripheral face of the wafer. Such imperfections result in stress points in the wafer's periphery that cause crazing or cracking in the wafer, and sometimes result in breaking off small particles from the wafer which migrate onto the surface of the wafer as contaminant particles, as discussed above. This entire problem is enhanced when gas is injected into a space between the backside of the wafer and the pedestal. Such gas, which is usually an inert gas such as Argon, is used to ensure uniform heating of the wafer and results in additional pressure being applied between the wafer's periphery and the clamp ring.
It would therefore be highly desirable to improve the clamping process and associated clamp ring in a manner that would reduce the type of product defects discussed above.